1. Field of the Invention
This invention relates to curable epoxy resins having increased adhesive strength; and, more particularly, to amine cured epoxy resins containing certain amino terminated polyether ureylene additives.
2. Prior Art
Epoxy resins constitute a broad class of polymeric materials having a wide range of physical characteristics. The resins are characterized by epoxide groups which are cured by reaction with certain catalysts or curing agents to provide cured epoxy resin compositions with certain desirable properties. One such class of curing agents is, generally, the amines. The most commonly used amine curing agents are aliphatic amines such as diethylenetriamine, triethylenetetramine and the like and/or polyoxyalkylene polyamines; such as polyoxypropylenediamines and triamines.
Epoxy resin compositions having improved physical properties are obtained by employing polyoxyalkyleneamines, and polyoxyalkylenediamines in particular, as curing agents. It is common to employ with such epoxy resin compositions a co-curing agent such as those described in U.S. Pat. No. 3,549,592.
Also known to be effective as epoxy curing agents or co-curing agents are various ureas and substituted ureas, such as those disclosed in U.S. 3,294,749, U.S. Pat. Nos. 2,713,569, 3,386,956, 3,386,955, 2,855,372 and 3,639,338. The ureas disclosed in the above references are useful as either curing agents or as curing accelerators.
It has now been unexpectedly found that specific amine terminated polyoxyalkylene containing ureylenes having a molecular weight of from about 4000 to about 4500, when employed as an epoxy additive/curing agent, provide cured epoxy resin compositions exhibiting outstanding strength of adhesion. Specifically, epoxy resins incorporating these additive/curing agents, upon curing, preferably in the presence of an additional amine curing agent, provide a material with high tensile shear strength and superior adhesion to substrates.
The results of incorporating the additives of the instant invention are particularly surprising in light of the fact that similar amine terminated ureylene compounds of lower molecular weight do not effect the same improvement in the cured resin. The cured epoxy resin compositions of the instant invention are useful as coatings, castings, sealants and, especially, adhesives.